ASR fault - wiring harness?

[B500EWF]

Hello everyone,

The car in question is a 1995 E500 with approximately 128,000 km on the odometer.

I come to you with a very annoying issue: the ASR light comes on as soon as I start up the engine and the revs at idle are limited to approx. 500 rpm. Additionally, pressing the acceleration pedal has no effect for approximately the first half of the pedal stroke, until I encounter increased physical resistance - the engine revs only if I push through that resistance. Please note that no other light in the dash comes on (including the ABS light, which I saw sometimes accompanies that ASR light).

I went to a mechanic and ran the STAR diagnostic tool on the engine and got multiple faults, as per the pictures attached. Now, the guy who ran the diagnostic tool is fairly certain that this is caused by a wiring harness malfunction (since this MY is known for its dubious biodegradable harnesses). However, from a previous check, I was able to confirm that the upper wiring harness (please see in attached pic) was replaced post-2011 with a Delphi component. The harness in question (where I was able to check that) is located in the upper left corner, next to the round diagnostic port. I was not able to verify whether the throttle body harness and the lower harness were indeed replaced as well.

My question to you guys is: since the upper wiring harness was replaced, do you also think that the throttle body harness is the main culprit for this? Or could it be something else?

Please don't hesitate to ask me for additional details which I may have skipped.

Thank you very much in advance!

 

[gsxr]

I come to you with a very annoying issue: the ASR light comes on as soon as I start up the engine and the revs at idle are limited to approx. 500 rpm. Additionally, pressing the acceleration pedal has no effect for approximately the first half of the pedal stroke, until I encounter increased physical resistance - the engine revs only if I push through that resistance. Please note that no other light in the dash comes on (including the ABS light, which I saw sometimes accompanies that ASR light).

If you have limp mode immediately upon starting the engine... that's a "hard" fault with the ETA (Electronic Throttle Actuator), aka 'EFP'. Or possibly E-GAS module (N4/1) which controls the ETA.

I went to a mechanic and ran the STAR diagnostic tool on the engine and got multiple faults, as per the pictures attached. Now, the guy who ran the diagnostic tool is fairly certain that this is caused by a wiring harness malfunction (since this MY is known for its dubious biodegradable harnesses).

It could be the wiring to the ETA itself. What is the date code on the ETA (click here)? If original and never rebuilt, that could be the problem. Note that your E500's original ETA will have bad / biodegradable wiring, however simply replacing the wiring may or may not fix the problem. There are internal components inside the ETA which can wear out or fail. It's worth a try though.

However, from a previous check, I was able to confirm that the upper wiring harness (please see in attached pic) was replaced post-2011 with a Delphi component. The harness in question (where I was able to check that) is located in the upper left corner, next to the round diagnostic port. I was not able to verify whether the throttle body harness and the lower harness were indeed replaced as well.

The engine wiring harness you have is good. This IS NOT the problem with your car. The engine harness is completely separate from the ETA system. The engine harness goes to the injectors, MAF, and some sensors. It has zero connection to the ETA.

My question to you guys is: since the upper wiring harness was replaced, do you also think that the throttle body harness is the main culprit for this? Or could it be something else?

Based on your fault codes, the #1 suspect is your ETA. However, it's also possible your E-GAS module (N4/1) could be faulty... or that both ETA and E-GAS are bad (a defective ETA could kill the E-GAS module, although this isn't common).

Ignore code 30 on ASR, that's a "ghost code" which appears every time limp mode is triggered. Also ignore the LH and EZ1 codes which are unrelated. Clear all those codes, if not already cleared. You'll probably get the same codes returning on E-GAS / EFP until the problem is fixed.


BTW - welcome to the forum!

 

[B500EWF]

Thank you so much for the response. I will share the info with my mechanic. One question about the misfire code (EZ1, I believe) - would it be possible that the overall poor running of the engine due to the trouble with the ASR fault (ETA etc.) could cause that misfire? One thing to mention here is that this is not a residual error code, as all codes have been cleared and the misfire EZ1 code reappeared. Or is it more likely to be caused by a bad spark plug/spark plug connector/coil? Is it worth going on that route? As far as I know, the spark plugs were replaced recently.

 

[B500EWF]

Also (and sorry to pester you with all sorts of questions), could you direct me to a resource (similar to the one above about the ETA code) where it is explained how to check whether the other wiring harnesses have been replaced or not? Thank you.

 

[gsxr]

Thank you so much for the response. I will share the info with my mechanic. One question about the misfire code (EZ1, I believe) - would it be possible that the overall poor running of the engine due to the trouble with the ASR fault (ETA etc.) could cause that misfire? One thing to mention here is that this is not a residual error code, as all codes have been cleared and the misfire EZ1 code reappeared. Or is it more likely to be caused by a bad spark plug/spark plug connector/coil? Is it worth going on that route? As far as I know, the spark plugs were replaced recently.

It usually requires a persistent misfire to trigger the fault code on the EZL (EZ1). You would notice the engine running on 7 cylinder with rough idle, rough operation under load, and reduced power. Definitely inspect the entire secondary ignition system to see what's going on there. This is a completely separate, unrelated problem vs the throttle issues with ETA/E-GAS.

Also (and sorry to pester you with all sorts of questions), could you direct me to a resource (similar to the one above about the ETA code) where it is explained how to check whether the other wiring harnesses have been replaced or not? Thank you.

There are only 3 harnesses:

• Upper engine harness (yours is good, date code 2011)
• Lower engine harness (connects to starter, alternator, oil pressure sender, oil level switch)
• Wiring pigtail attached to the ETA / throttle body (click the link in my previous post to see how to read the date code).

Your lower harness may be old / original, but would not cause any of the faults you are experiencing.

 

[B500EWF]

Thank you again for the answer. It probably is best to address the ASR issue first and then start with troubleshooting this one, with the misfire. I will also check the code on the throttle nody harness.